Method of making magnetic cores



March 3, 1964 K. D. BEARDSLEY ETAL 3,122,821

METHOD OF MAKING MAGNETIC CORES 2 Sheets-Sheet 1 Filed March 28, 1958 March 3, 1964 K. D. BEARDSLEY ETAL 3,122,321

METHOD OF MAKING MAGNETIC CORES Filed March 28, 1958 2 Sheets-Sheet 2 i l! i L- J L- l 27 EVE fir 3 222 53553??? ilnited This invention relates to wound magnetic cores and more particularly to an improved method of cutting wound magnetic co es preparatory to linking the same with electrical coils.

One well known form of such core is shown in prior Vienneau Patent 2,305,649. One method of making such a core is to spirally wind a strip of magnetic material into a blur of superposed turns on a mandrel. After the rct ulred number of turns are wound the core is banded or otherwise clamped and then placed in an annealing furnace to give its turns a permanent set and to relieve the stresses which wer introduced into the strip during the winding operation. The core can be annealed while it is on its mandrel although this is not absolutely necessary inasmuch as other means can be utilized to hold the core in its required shape while it is in the annealing furnace. After the core comes out of the annealing furnace theoreticallv it is in its ideal condition inasmuch as all of the which were introduced in the strip during the windion have been relieved. Therefore, the next step electrical coil with a sum of distortion in the strip so as not to introduce strains into the strip. There are several ways of doing this, however they have not been entirely successful and have several practical disadvantages.

Q e metnod is to unwind the annealed core starting wit its outer turns and progressively cut the strip into s ments of approximately one or two turn lengths of the core. One disadvantage of this method is that the core must be entirely out before it can be laced or linked with an electrical coil. After the core is entirely out then th segments are linked with the electrical coil inversely from the order in which they were cut. That is, due to the necessity of entirely cutting the core before lacing can commence there is a period of delay in the manufacturing cycle between the cutting step and the lacing step. Additionally this method of manufacture may require a large a unt of manufacturing space or the like inasmuch as the cut segments need to be laid aside or temporarily stored unti such time as the core is completely out and lacing can commence. The amount of manufacturing space req "ed can be reduced by telescoping the segme ts into a single stack as they are cut.

is to link or lace the core with an However, during lacing the segments must be separated from the stack and this is not convenient to do since the telescoped segments tend to stick together and they are dilficult to grip since they are thin and the assembler conventionally works with heavy gloves. Another disadvantage of this method is that the step of unwinding the core may introduce strains into the annealed strip.

Another prior art method of linking a strip wound annealed core with an electrical coil is to omit cutting the core and instead to bring he outer end of the strip through the window of an electrical coil and then to rotate the core until it has been expanded into a larger magnetic core loop as compared to its size after anneal. After this is accomplished the inner end of the strip is brought around one or" the legs of the electrical coil and then the large magnetic core loop is collapsed about the electrical coil leg. One form of this method is shown in prior Granfield Patent 2,160,588. One disadvantage of such method is that it requires special apparatus to practice it. Additionally, due to the amount of handling required to first and then collapse the core the intro- ?itates Fascist ice 2 duction of stresses in the annealed strip is difficult to avoid. Furthermore special care must be taken to insure that the core strip does not introduce flaws by abrasion or the like in the insulation on the electrical coils.

Another A rior art method of linking a strip wound anneared magnetic core with an electrical coil without cutting the s 'ip into segments is disclosed in prior Boyajian Patent 2,245,180. in this patent the annealed magnetic core is not expanded into a larger core loop but is expanded into a cone after which the strip can be laced about a leg of the electrical coil starting with the inner end of the core strip. However, the disadvantages of this ad are similar to those outlined above with respect the thod of Granfield 2369,5238. Another prior art method in which the annealed core is cut into segments is disclosed in prior Acly Patent 1,935,426. in this patent the core strip is not unwound for cutting. Instead the wound core is out completely through at one of its parts and then alternate turns are reversed with respect to the remaining turns in order to have the butt joints in adjacent layers offset or staggered with respect to each other. However, one of the practical disadvantages or" this method is that the requirement for reversal of alternate turns increases labor costs. Also, inasmuch as after they are reversed the turns do not have the same disposition with respect to each other which they had in the annealed uncut core difiiculty is sometimes encountered in closing the butt joints and obtaim'ng compact superimposed turns. The butt joints in such a case be forcibly closed, but this may result in straining the annealed strips. Additionally, the necessity for reversal increases the amount of handling of the strips and opportc lity for introducing deformations and strains therein.

it is an object of this invention to provide an improved method of cutting strip wound magnetic cores and linking the same with electrical coils which will overcome the disadvantages of the above described exemplary prior art methods.

In the preferred form of the invention the annealed wound core is progressively cut in staggered or olfset fashion by starting at the inside of the core and worxing towards its outside. This procedure permits immediate lacing or linking of the core with the electrical coil. Additionally it minimizes the amount of deformations and strains which be introduced in the annealed strip. Furthermore this method requires less manufacturing space and capital investment and special equipment.

The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. Our invention, however, both as to organization and method of operation, together v further obects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates the method step of form winding a strip of magnetic material into a magnetic core;

FIG. 2 illustrates one sequence of cutting the magnetic core of 1 16.1 after it has been annealed;

PEG. 3 illustrates the method of lacing the segments of the magnetic core of FIG. 2 with an electrical coil;

FIG. 4 illustrates another cutting sequence which may be employed; and

FIG. 5 illustrates the method of lacing the segments of FlG. 4 with an electrical coil.

Referring now particularly to FIG. 1 of the drawings, in the preferred form of our invention the strip of magnetic material 1 is wound on a mandrel 2 which has the same configuration as that desired in the final core. After the required number of turns are wound on the mandrel 2 the core is banded or otherwise clamped and placed in an 3 annealing furnace along with its mandrel to give a permanent set to the turns and to remove the strains and deformations which were introduced in the strip 1 during the winding procedure.

Preferably the strip 1 has its grains oriented lengthwise of the strip so as to eliminate cross grain efiect of the magnet flux in the core. The strip 1 may have a thin electrical insulating material coating formed thereon for a purpose which is Well known in the art, and it can be wound on the mandrel 2 with a slight amount of looseness or space between turns in order to facilitate lacing of the magnetic core with an electrical coil after the core has been annealed and cut. A thin paper spacer can be simultaneously wound with the strip 1 to provide the spacing between turns. The paper spacer will be burned when the core is in the annealing furnace and the ashes can be later removed by high pressure air jets. However, other means could be employed for obtaining the desired amount of spacing between turns. For instance, shims could be inserted between every several turns, or the core could be wound without high tension. Also, spaces between turns could be provided by forming small bumps in the strip in accordance with the teachings of our pending patent application Serial No. 65 6,254 which was filed on May 1, 1957, now Patent No. 3,027,628, granted April 3, 1962, and is assigned to the same assignee as the instant patent application.

The investment is not restricted to form winding the strip 1 on a form or mandrel which has the same configuration as that desired in the final core. F or instance, the strip 1 could be wound on a circular mandrel and thereafter the circular wound core could be formed or shaped by suitable pressing means into a rectangular shape in the event a rectangular shape is desired in the final magnetic core. Additionally, the core does not necessarily have to be annealed while it is on its mandrel 2, but the mandrel 2 could be removed after the winding operation and other means could be employed to brace and retain the wound turns in a rectangular shape while they are in the annealing furnace. After the continuously spirally wound core is annealed the mandrel 2 and clamping band or other equivalent means is removed from the core and then the core is cut into segments by starting from the inside of the core and working outwardly. This permits immediate lacing of the strip with the electrical coil instead of waiting until the core is entirely cut. The strip can be cut into any desired number of pieces. For instance, it can be cut into one half turn segments, or lengths of slightly less than or more than one turn, or one and one half turn segments, or lengths of slightly less than or more than two turns. Obviously a shorter segment will be easier to handle and lace with the electrical coil than a longer segment such as one which is two or three turns long. However, short se ments require a greater number of cuts in the core which increases the core reluctance. Regardless of which length is decided upon successive cuts in the core are oifset or staggered with respect to each other so as to have the butt joints in each layer of the core lapped by continuous strip in adjacent layers of the core. The offset cuts can be arranged along the legs or yokes of the core, or they can progress continuously about the core as successive segments are cut. Aside from the requirement for offset between adjacent cuts the particular location of the cuts in the core will be dictated in part by the ease with which the cut segment can be linked with the electrical coil. That is, with a minimum amount of handling and opportunity for the introduction of deformations and strains in the segments during the time they are linked or laced with the electrical coil.

In the arrangement shown in FIG. 2 cutting is commenced at the inner turn at the upper end of a core leg and progresses along the leg until the lower end of the core leg is reached, and then the same sequence is repeated. This gives the segments a length of slightly greater than one turn which facilitates their lacing with d the electrical winding cylinder or coil 3 as illustrated in FIG. 3. Obviously if cutting were commenced at the lower end of a core leg the segments would have a length of slightly less than one full core turn.

The winding coil 3 in FIG. 3 comprises primary and secondary electrical winding sections as is well known in the art. The electrical apparatus illustrated in FIG. 3 utilizes two core sections. The butt joints in the core sections are placed in the legs thereof which are disposed inside the electrical coil so as to facilitate lacing of the segments of the core with the coil. However, this is not absolutely necessary and the butt joints could be located in other parts of the core sections.

For instance, in the cutting arrangement illustrated in FIG. 4 the core is also cut by starting at the inside and progressing towards the outside of the core. Adjacent cuts are ofiset or staggered with respect to each other. However, they are located in a yoke portion of the core. The manner of lacing the segments of the cut strip with an electrical winding is illustrated in FIG. 5. The electrical apparatus of FIG. 5 utilizes two electrical winding cylinders, each of which may contain primary and secondary winding sections.

In both forms of the invention the cut segments of the core have the same disposition with respect to each other in the final core as they had before the annealed core was cut. That is, no reversal of the turns or segments is required. This makes for a more compact and more easily assembled core inasmuch as sometimes when the turns or segments are reversed with respect to each other as in the previously mentioned Acly patent they do not prefectly match. For instance, a mismatch may occur due to the fact that reversed corners of the rectangular shaped core are not exactly identical. Additionally, in the invention the turns do not actually need to be unwound from the inside of the core since they can be cut while they are still located inside the core. This is an advantage inasmuch as it serves to reduce the degree to which the strip may be distorted by handling from the time the strip comes out of the annealed furnace to the time that it is laced with the electrical coil. However, it is within the scope of the invention to unwind and cut the annealed core from the inside or to expand it into a larger shape of fewer turns and then to cut it starting with the inner turns since these methods also provide the several advantages of our invention although possibly not to the same degree as when the turns are cut while they are still located inside the core. Unwinding the core and cutting it from the inside or expanding it into a larger shape of fewer turns and then cutting it from the inside may be required where there is not enough working space in the core window for the shear tool which is used to cut the strip. However,

cutting of the core can be done with small hand or machine operated shear tools in which event it would not be necessary to unwind or expand the core in order to cut the strip.

The invention is useful in making stationary electrical induction apparatus which utilize wound cores and electrical windings which are linked with each other. EX- amples of such apparatus are transformers and reactors.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore, it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A method of making a magnetic core which has a window opening and linking the same with a preformed electrical coil which has a window opening, said method comprising spirally winding a flat strip of magnetic material on a mandrel which has a generally rectangular shape into a plurality of generally rectangular shaped and radially superposed turns, then retaining the wound turns closed on t e mandrel with retaining means and annealing them while they are on the mandrel to give their generally rectangular shape a permanent set, then removing the retaining means and the mandrel from the annealed turns, then cutting the strip of magnetic material into successive segments by progressively cutting it from its inner end toward its outer end, the successive segments being cut so that the cuts in any turn of the core are circumferentially ofiset from the cuts in adjacent turns, the successive segments being cut one at a time and without unwinding of the strip by cutting the strip while the successive segments are nested in the same position as they had on the mandrel and while its inner end is still located inside the core substantially in its annealed position, then lifting each segment from inside the core after it is cut and lacing it with the preformed electrical coil in the same position it had with respect to the other segments of the annealed core, and each segment being laced with the preformed electrical coil while its immediately successive segment is being cut.

2. A method of making a magnetic core which has a window opening and linking the same with a preformed electrical coil which has a window opening, said method comprising spirally winding a flat strip of magnetic material on a generally rectangular shaped mandrel into a plurality of generally rectangular shaped and radially superposed turns, then retaining the wound turns closed with retaining means and annealing them while they are on the mandrel to give their generally rectangular shape a permanent set, then removing the retaining means and the mandrel from the annealed turns, then cutting the strip of magnetic material into successive segments by progressively cutting it from its inner end toward its outer end, the successive segments being cut one at a time and without unwinding of the strip by cutting the strip while the successive segments are nested in the same position as they had on the mandrel and while its inner end is still located inside the core substantially in its wound and annealed position, and then lifting each segment from inside the core after it is cut and lacing it with the preformed electrical coil while its immediately successive segment is being cut.

3. A method of making a magnetic core which has a window opening and linking the same with a preformed electrical coil which has a window opening, said method comprising spirally Winding a fiat strip of magnetic material on a winding mandrel into a plurality of radially superposed turns, annealing the Wound turns while they are on the winding mandrel, removing the winding mandrel from the annealed turns, cutting the strip of magnetic material into successive segments by starting at its inner end and progressing toward its outer end, the sucessive segments being cut one at a time and without unwinding of the strip by cutting the strip while the successive segments are nested in the same position as they had on the mandrel and while its inner end is still located inside the core, and lifting each cut segment from inside the core and lacing it with the preformed electrical coil while its immediately successive segment is being cut.

4. A method of making a magnetic core which has a window opening and linking the same with a preformed electrical coil which has a window opening, said method comprisin spirally Winding a flat strip of magnetic material cn a mandrel into a wound core having a plurality of radially superposed turns, annealing the wound turns and removing the core from the mandrel, cutting the strip of magnetic material into successive segments by starting at its inner end and progressively cutting it toward its outer end, the successive segments being cut one at a time and Without unwinding of the strip by cutting the strip while the successive segments are nested in the same position as they had on the mandrel and while its inner end is still located inside the wound core substantially in its wound and annealed position, and lifting each segment from inside the wound core after it is cut and lacing it with the preformed electrical coil While its immediately successive segment is being cut.

5. A method of making a magnetic core which has a window opening and linking the same with a preformed electrical coil which has a window opening, said method comprising providing a spirally wound core of flat strip magnetic material having a plurality of radially superposed turns, heat treating the wound core, cutting the strip of magnetic material into successive segments by starting at its inner end and progressively cutting it toward its outer end, the successive segments being cut one at a time and without unwinding of the strip by cutting the strip while the successive segments are nested substantially in the same position as they had in the wound core while being heat treated and while its inner end is still located inside the wound core, and lifting each segment from inside the wound core after it is cut and lacing it with the preformed electrical coil while its immediately successive segment is being cut.

References (Iited in the file of this patent UNITED STATES PATENTS 1,935,426 Acly Nov. 14, 1933 2,160,588 Granfield May 30, 1939 2,245,180 Boyajian June 10, 1941 2,305,649 Vienneau Dec. 22, 1942 2,305,650 Vienneau Dec. 22, 1942 2,344,294 Evans Mar. 14, 1944 2,655,717 Dunn Oct. 20, 1953 2,657,456 Moody Nov. 3, 1933 2,700,207 Zimsky Jan. 25, 1955 FOREIGN PATENTS "96,346 Great Britain Aug. 26, 1953 

5. A METHOD OF MAKING A MAGNETIC CORE WHICH HAS A WINDOW OPENING AND LINKING THE SAME WITH A PREFORMED ELECTRICAL COIL WHICH HAS A WINDOW OPENING, SAID METHOD COMPRISING PROVIDING A SPIRALLY WOUND CORE OF FLAT STRIP MAGNETIC MATERIAL HAVING A PLURALITY OF RADIALLY SUPERPOSED TURNS, HEAT TREATING THE WOUND CORE, CUTTING THE STRIP OF MAGNETIC MATERIAL INTO SUCCESSIVE SEGMENTS BY STARTING AT ITS INNER END AND PROGRESSIVELY CUTTING IT TOWARD ITS OUTER END, THE SUCCESSIVE SEGMENTS BEING CUT ONE AT A TIME AND WITHOUT UNWINDING OF THE STRIP BY CUTTING THE STRIP WHILE THE SUCCESSIVE SEGMENTS ARE NESTED SUBSTANTIALLY IN THE SAME POSITION AS THEY HAD IN THE WOUND CORE WHILE BEING HEAT TREATED AND WHILE ITS INNER END IS STILL LOCATED INSIDE THE WOUND CORE, AND LIFTING EACH SEGMENT FROM INSIDE THE WOUND CORE AFTER IT IS CUT AND LACING IT WITH THE PREFORMED ELECTRICAL COIL WHILE ITS IMMEDIATELY SUCCESSIVE SEGMENT IS BEING CUT. 